1. Field of the Invention
The present invention relates an image forming apparatus and particularly to a structure for preventing particle accumulation on an image-density sensor due to, for example, toner adhesion.
2. Discussion of the Background
In an image forming apparatus, such as a copier, a printer, a facsimile machine, and a printing machine, a visible image formed on a photoconductor serving as an image bearing member for an electrostatic latent image is transferred to a recording medium, such as a sheet of paper, thereby creating a final copy.
Images on the final copy are printed in monochrome color or in multiple colors, such as in full color. To obtain a monochrome image, an image processing unit includes an image bearing member for a single electrostatic latent image and its corresponding electrifying device, writing device, developing device, and transfer device. To obtain a multicolor image, for example, tandem type image processing units capable of forming images in respective colors are used.
In an image forming apparatus including tandem type image processing units for obtaining a full color image, a belt movable while being kept in contact with photoconductors in the respective image processing units functions as an intermediate transfer member. In a primary transfer process, images formed in the respective image processing units are sequentially transferred to the intermediate transfer member to superimpose the images thereon. The superimposed images are then simultaneously transferred to a recording medium in a secondary transfer process.
In an image forming apparatus, the image density may change depending on changes in the operating environment and the number of copies performed. Since changes in colors are particularly noticeable in color images, attempts to maintain uniform density have been made. For example, patch images in respective colors are formed on an intermediate transfer member to detect the density of each patch image by an optical density sensor. Then, image forming conditions, such as electrifying conditions and developing conditions, are adjusted depending on the result of the detection.
If the optical density sensor as described above is used as a density sensor, particles remaining on a detection window due to, for example, toner adhesion may interfere with accurate detection. Paper dust generated due to, for example, a paper jam may contaminate the detection window to interfere with accurate detection.
Possible approaches to prevent particles from remaining on the detection window include applying airflow from a cooling fan installed in an image forming apparatus to the surface of the detection window, installing or preparing a user-operable cleaning tool, and carrying out periodic cleaning by service engineers.
The above-described approaches are effective if the image forming apparatus has space for installing a cleaning unit. However, it is difficult to take such approaches in a space-saving type apparatus, which is required these days.
For example, an image forming apparatus may not have enough space for installation of a duct that introduces airflow, or, even if the duct is installed, the duct may not be capable of securing the airflow required for removing particles. In addition, space for inserting someone's hands for a cleaning operation cannot be secured. Moreover, the cleaning operation itself is a cumbersome task and may not be carried out very frequently. This causes toner accumulation and interferes with complete removal of particles. Furthermore, installation of a cleaning tool not only causes an increase in cost but also causes loss of time for the image forming operation during the cleaning operation performed by service engineers. If a user is involved in the cleaning operation, in this case, such a cumbersome task may not be carried out frequently and may cause problems as described above.